U.S. patent application number 16/084567 was filed with the patent office on 2019-02-21 for method for manufacturing a turbine shroud for a turbomachine.
This patent application is currently assigned to SAFRAN AIRCRAFT ENGINES. The applicant listed for this patent is CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE, SAFRAN AIRCRAFT ENGINES, UNIVERSITE PAUL SABATIER - TOULOUSE III. Invention is credited to Yannick Marcel BEYNET, Geoffroy CHEVALLIER, Romain EPHERRE, Claude ESTOURNES, Jean-Baptiste MOTTIN.
Application Number | 20190054537 16/084567 |
Document ID | / |
Family ID | 56511658 |
Filed Date | 2019-02-21 |
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United States Patent
Application |
20190054537 |
Kind Code |
A1 |
MOTTIN; Jean-Baptiste ; et
al. |
February 21, 2019 |
METHOD FOR MANUFACTURING A TURBINE SHROUD FOR A TURBOMACHINE
Abstract
The invention relates to a method for manufacturing a turbine
shroud (24) for a turbomachine, the method comprising manufacturing
at least one turbine shroud sector (28), positioning the turbine
shroud sector (26) in a bottom mold so that an outer surface of the
turbine shroud sector is in contact at least in part with the
bottom mold, and depositing a powder layer on an inner surface (28)
of the turbine shroud sector (26). Thereafter, a top mold is
positioned on the powder layer and an abradable layer (32) is made
by subjecting the powder layer to a method of SPS sintering, the
abradable layer (32) being for being disposed facing a turbine
wheel.
Inventors: |
MOTTIN; Jean-Baptiste;
(Moissy-Cramayel, FR) ; BEYNET; Yannick Marcel;
(Toulouse, FR) ; CHEVALLIER; Geoffroy;
(Auzeville-Tolosane, FR) ; EPHERRE; Romain;
(Toulouse, FR) ; ESTOURNES; Claude; (Rieumes,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SAFRAN AIRCRAFT ENGINES
CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE
UNIVERSITE PAUL SABATIER - TOULOUSE III |
Paris
Paris
Toulouse |
|
FR
FR
FR |
|
|
Assignee: |
SAFRAN AIRCRAFT ENGINES
Paris
FR
CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE
Paris
FR
UNIVERSITE PAUL SABATIER - TOULOUSE III
Toulouse
FR
|
Family ID: |
56511658 |
Appl. No.: |
16/084567 |
Filed: |
March 10, 2017 |
PCT Filed: |
March 10, 2017 |
PCT NO: |
PCT/FR2017/050546 |
371 Date: |
September 13, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 7/08 20130101; F05D
2230/22 20130101; B22F 2003/247 20130101; B22F 2301/15 20130101;
F05D 2240/11 20130101; B22F 7/06 20130101; F01D 11/122 20130101;
B22F 3/105 20130101; B22F 3/24 20130101; F05D 2230/61 20130101;
B22F 2207/01 20130101; B22F 5/009 20130101; F01D 9/04 20130101 |
International
Class: |
B22F 5/00 20060101
B22F005/00; B22F 7/08 20060101 B22F007/08; B22F 3/24 20060101
B22F003/24; B22F 3/105 20060101 B22F003/105; F01D 9/04 20060101
F01D009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2016 |
FR |
1652102 |
Claims
1. A method for manufacturing a turbine shroud for a turbomachine,
the method comprising the following steps: manufacturing at least
one turbine shroud sector; positioning the turbine shroud sector in
a bottom mold so that an outer surface of the turbine shroud sector
is in contact at least in part with the bottom mold; depositing a
powder layer on an inner surface of the turbine shroud sector;
positioning a top mold on the powder layer; and making an abradable
layer on the inner surface by subjecting the powder layer to a
method of SPS sintering, the abradable layer being for being
disposed facing a turbine wheel.
2. A method according to claim 1, further comprising the following
steps: assembling together a plurality of turbine shroud sectors,
the inner surface of each turbine shroud sector being covered in an
abradable layer; and machining a free surface of the abradable
layer.
3. A method according to claim 1, wherein the bottom mold is of
shape complementary to the outer surface of the turbine shroud
sector.
4. A method according to claim 1, wherein before positioning the
turbine shroud sector in the bottom mold and the top mold, a layer
of chemically inert material is deposited on the bottom mold and on
the top mold.
5. A method according to claim 1, wherein the powder is a metal
powder based on cobalt or on nickel.
6. A method according to claim 1, wherein the SPS sintering is
performed for a duration shorter than or equal to 60 minutes.
7. A method according to claim 1, wherein the top mold and the
bottom mold are made of graphite, and wherein the SPS sintering is
performed at a temperature higher than or equal to 800.degree.
C.
8. A method according to claim 7, wherein the SPS sintering is
performed at a pressure higher than or equal to 10 MPa.
9. A method according to claim 1, wherein the top mold and the
bottom mold are made of tungsten carbide, and wherein the SPS
sintering is performed at a temperature higher than or equal to
500.degree. C.
10. A method according to claim 9, wherein the SPS sintering is
performed at a pressure higher than or equal to 100 MPa.
Description
BACKGROUND OF THE INVENTION
[0001] The present disclosure relates to a method for manufacturing
a turbine shroud for a turbomachine.
[0002] In numerous rotary machines, it is now known to provide the
ring of the stator with abradable tracks facing the tips of the
blades of the rotor. Such tracks are made using so-called
"abradable" materials, which, when they come into contact with
rotating blades, become worn more easily than the blades
themselves. This serves to ensure minimum clearance between the
rotor and the stator, thereby improving the performance of the
rotary machine, without running the risk of damaging the blades in
the event of them rubbing against the stator. On the contrary, such
rubbing erodes the abradable track, thereby acting automatically to
match the diameter of the shroud of the stator as closely as
possible to the rotor. Thus, such abradable tracks are often
installed in turbomachine compressors.
[0003] In contrast, use of such tracks is less common in the
turbines of such turbomachines, and in particular in the high
pressure turbines in which physico-chemical conditions are
extreme.
[0004] Specifically, the burnt gas coming from the combustion
chamber flows into the high-pressure turbine at very high levels of
temperature and pressure, thereby leading to premature wear of
conventional abradable tracks.
[0005] Under such circumstances, in order to protect the turbine
shroud, it is often preferred to provide it with a thermal barrier
type coating made of materials that serve to protect the shroud
against erosion and corrosion and that present density that is
high, too high for the coating to be effectively abradable.
[0006] Nevertheless, under such circumstances, it can naturally be
understood that the integrity of the blades is no longer ensured in
the event of coming into contact with the stator, which makes it
necessary to provide greater clearance between the rotor and the
stator, and therefore increases the rate of leakage past the tips
of the blades, thus reducing the performance of the turbine.
OBJECT AND SUMMARY OF THE INVENTION
[0007] The present disclosure seeks to remedy these drawbacks, at
least in part.
[0008] To this end, the present disclosure relates to a method
manufacturing a turbine shroud for a turbomachine, the method
comprising the following steps: [0009] manufacturing at least one
turbine shroud sector; [0010] positioning the turbine shroud sector
in a bottom mold so that an outer surface of the turbine shroud
sector is in contact at least in part with the bottom mold; [0011]
depositing a powder layer on an inner surface of the turbine shroud
sector; [0012] positioning a top mold on the powder layer; and
[0013] making an abradable layer on the inner surface by subjecting
the powder layer to a method of SPS sintering, the abradable layer
being for being disposed facing a turbine wheel.
[0014] The turbine shroud is generally made out of a plurality of
portions, each portion forming a turbine shroud sector of
dimensions that are small compared with the dimensions of the
complete turbine shroud. It is thus simple to place a shroud sector
in a mold.
[0015] The inner surface of the turbine shroud sector is the
surface that faces the turbine wheel when the turbine shroud is
mounted in the turbine, and it is thus this inner surface on which
the powder layer is deposited.
[0016] The SPS sintering method (SPS standing for "spark plasma
sintering") is also known as field assisted sintering technology
(FAST), or as flash sintering, and it is a method of sintering
during which a powder is subjected simultaneously to high-current
pulses and to uniaxial pressure in order to form a sintered
material. SPS sintering is generally performed under a controlled
atmosphere, and it may be assisted by heat treatment.
[0017] The duration of SPS sintering is relatively short, and SPS
sintering makes it possible to select starting powders with
relatively few limitations. Specifically, SPS sintering makes it
possible in particular to sinter, i.e. to densify, materials that
are relatively complicated to weld, or indeed impossible to weld,
because they are materials that crack easily when heated. As a
result of selecting SPS sintering and of the short duration of such
sintering, it becomes possible to make an abradable layer out of a
very wide variety of materials.
[0018] Furthermore, since SPS sintering is performed under uniaxial
pressure exerted on the powder layer by the bottom mold and the top
mold, the shrinkage of the powder layer that results from the
sintering for producing the abradable layer is restricted to the
direction in which pressure is applied. No shrinkage of the powder
layer is thus to be observed in directions perpendicular to the
direction in which pressure is applied. The abradable layer thus
covers the entire inner surface of the shroud sector.
[0019] The turbine shroud is thus covered in an abradable layer. It
is thus possible to make provision for the clearance between the
turbine shroud and the rotor, e.g. the blades of a turbine wheel,
to be relatively small, and to improve the performance of the
turbine, but without any risk of damaging the blades in the event
of them rubbing against the shroud of the stator.
[0020] Furthermore, SPS sintering enables a diffusion layer to be
formed between the abradable layer and the material forming the
shroud sector, such that the abradable layer is firmly attached to
the material forming the shroud sector. The abradable layer as
formed in this way cannot be removed from the shroud sector in
unintentional manner.
[0021] The method may further comprise the following steps [0022]
assembling together a plurality of turbine shroud sectors, the
inner surface of each turbine shroud sector being covered in an
abradable layer; and [0023] machining a free surface of the
abradable layer.
[0024] Once a plurality of these turbine shroud sectors have been
assembled together, the abradable layer of each shroud sector
presents a free surface that need not necessarily extend
continuously from the free surface of the adjacent shroud sector.
Thus, the free surfaces of the various shroud sectors are machined
so that the surface that is to face the turbine wheel presents as
little discontinuity as possible. Specifically, if any such
discontinuity is present, then the turbine wheel could strike
against such a discontinuity, thereby leading to impacts within the
turbine, which is not desirable.
[0025] The bottom mold may be of shape complementary to the outer
surface of the turbine shroud sector.
[0026] Thus, the bottom mold applies relatively uniform pressure
against the outer surface of the shroud sector. Nevertheless, since
the bottom mold presents a shape that is complementary to the outer
surface of the shroud sector, the mold makes it possible to
accommodate variations in dimensions from one shroud sector to
another due to the method for manufacturing a shroud sector.
Specifically, and by way of example, the turbine sectors may be
obtained by a casting method and the dimensions of each turbine
sector may vary a little from one turbine sector to another.
[0027] Before positioning the turbine shroud sector in the bottom
mold and the top mold, a layer of chemically inert material may be
deposited on the bottom mold and on the top mold.
[0028] This layer of chemically inert material makes it possible to
reduce chemical reactions between the powder layer and the turbine
shroud sector with the bottom mold and the top mold during SPS
sintering. The chemically inert material serves in particular to
reduce, or even to avoid, the layer of abradable material and/or
the shroud sector sticking to portions of the mold.
[0029] The chemically inert material also makes it possible to
reduce, or even to avoid, any formation of a carbide layer on the
free surface of the abradable layer. It is desirable to avoid
forming such a carbide layer, since any carbide layer that is
formed needs to be removed from the abradable layer before it is
used.
[0030] In the bottom mold, the chemically inert material may also
serve to fill in the gaps that exist between the bottom mold and
the outer surface of the turbine shroud sector. This improves the
uniformity of the pressure exerted by the bottom mold on the
turbine shroud sector and thus on the powder layer.
[0031] By way of example, the chemically inert material may
comprise boron nitride or corundum. When the chemically inert
material is said to "comprise" boron nitride, that is used to mean
that the material comprises at least 95% by weight boron nitride.
Likewise, when the chemically inert material is said to "comprise"
corundum, that is used to mean that the material comprises at least
95% by weight corundum.
[0032] The powder may be a metal powder based on cobalt or on
nickel.
[0033] The term "based on cobalt" is used to mean a metal powder in
which cobalt presents the greatest percentage by weight. Likewise,
the term "based on nickel" is used to mean a metal powder in which
nickel presents the greatest percentage by weight. Thus, by way of
example, a metal powder comprising 38% by weight cobalt and 32% by
weight nickel is referred to as a cobalt based powder, since cobalt
is the chemical element having the greatest percentage by weight in
the metal powder.
[0034] Cobalt- or nickel-based metal powders are powders that
present good high-temperature strength after sintering. They can
thus perform the two functions of being abradable and of providing
a heat shield. By way of example, mention may be made of CoNiCrAlY
superalloys. These metal powders also have the advantage of
presenting a chemical composition that is similar to the chemical
composition of the material forming the turbine shroud, e.g. AM1 or
N5 superalloy.
[0035] The SPS sintering may be performed for a duration that is
shorter than or equal to 60 minutes, preferably shorter than or
equal to 30 minutes, still more preferably shorter than or equal to
15 minutes.
[0036] The duration of SPS sintering is thus relatively short.
[0037] The top mold and the bottom mold may be made of graphite,
and the SPS sintering may be performed at a temperature higher than
or equal to 800.degree. C., preferably higher than or equal to
900.degree. C.
[0038] The SPS sintering may be performed at a pressure higher than
or equal to 10 megapascals (MPa), preferably higher than or equal
to 20 MPa, still more preferably higher than or equal to 30
MPa.
[0039] The top mold and the bottom mold may be made of tungsten
carbide, and the SPS sintering may be performed at a temperature
higher than or equal to 500.degree. C., preferably higher than or
equal to 600.degree. C.
[0040] The SPS sintering may be performed at a pressure higher than
or equal to 100 MPa, preferably higher than or equal to 200 MPa,
still more preferably higher than or equal to 300 MPa.
[0041] The abradable layer may have apparent porosity that is less
than or equal to 20%, preferably less than or equal to 15%, still
more preferably less than or equal to 10%.
[0042] By using the SPS sintering method, it is possible to vary
sintering parameters such as pressure, sintering temperature,
and/or sintering time, so as to vary the porosity of the resulting
abradable layer. This method for manufacturing a turbine shroud for
a turbomachine thus provides great flexibility.
[0043] The abradable layer may present thickness that is greater
than or equal to 0.5 millimeters (mm), preferably greater than or
equal to 4 mm, and less than or equal to 15 mm, preferably less
than or equal to 10 mm, still more preferably less than or equal to
5 mm.
[0044] The number of turbine shroud sectors in the turbine shroud
may be greater than or equal to 20, preferably greater than or
equal to 30, still more preferably greater than or equal to 40.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] Other characteristics and advantages of the invention appear
from the following description of implementations of the invention,
given as nonlimiting examples, and with reference to the
accompanying figures, in which:
[0046] FIG. 1 is a diagrammatic longitudinal section view of a
turbomachine;
[0047] FIG. 2 is a diagrammatic perspective view of a turbine
shroud sector including an abradable layer;
[0048] FIG. 3 is a section view of a turbine shroud sector in a
mold for SPS sintering, the section plane being similar to the
section plane III-III of FIG. 2;
[0049] FIGS. 4A and 4B are diagrammatic side views of a plurality
of turbine shroud sectors covered in an abradable layer,
respectively before and after machining a free surface of the
abradable layer;
[0050] FIG. 5 is a scanning electron microscope image of an
interface between a shroud sector and an abradable layer;
[0051] FIG. 6 shows how the concentration of certain chemical
elements varies in the abradable layer of the shroud sector;
and
[0052] FIGS. 7A-7D are scanning electron microscope images showing
the microstructure of the various abradable layers.
DETAILED DESCRIPTION OF THE INVENTION
[0053] FIG. 1 shows a bypass jet engine 10 seen in section on a
vertical plane containing its main axis A. From upstream to
downstream in the flow direction of the air stream, the bypass jet
engine 10 comprises a fan 12, a low-pressure compressor 14, a
high-pressure compressor 16, a combustion chamber 18, a
high-pressure turbine 20, and a low-pressure turbine 22.
[0054] The high-pressure turbine 20 has a plurality of blades 20A
that rotate with the rotor, and vanes 20B that are mounted on the
stator. The stator of the turbine 20 has a plurality of stator
shrouds 24 arranged facing the blades 20A of the turbine 20.
[0055] As can be seen in FIG. 2, each stator shroud 24 is made up
of a plurality of shroud sectors 26. Each shroud sector 26 has an
inner surface 28, an outer surface 30, and an abradable layer 32
against which the blades 20A of the rotor come into rubbing
contact.
[0056] By way of example, the shroud sector 26 is made of a cobalt-
or nickel-based superalloy, such as the AM1 superalloy or the N5
superalloy, and the abradable layer 32 is obtained from a metal
powder based on cobalt or on nickel.
[0057] The method for manufacturing the turbine shroud 24 includes
a first step for manufacturing at least one turbine shroud sector
26, e.g. by using a casting method.
[0058] FIG. 3 shows the turbine shroud sector 26 in section view in
a mold for SPS sintering. The mold includes a bottom mold 34 of
shape that is complementary to the outer surface 30 of the shroud
sector 26.
[0059] The shroud sector 26 is positioned in a bottom mold 34 so
that the outer surface 30 of the shroud sector 26 is in contact, at
least in part, with the bottom mold 34. The bottom mold 34 is thus
not in contact with the shroud sector 26 over the entire outer
surface 30 of the shroud sector 26. The gaps visible between the
shroud sector 26 and the bottom mold 34 serve to accommodate
dimensional variations due to the method for manufacturing the
various shroud sectors 26.
[0060] Nevertheless, since the shape of the bottom mold 34 is
complementary to the outer surface 30 of the shroud sector 26, the
pressure exerted by the bottom mold 34 on the shroud sector 26 is
relatively uniform.
[0061] Thereafter, a powder layer 36 is deposited on the inner
surface 28 of the shroud sector 26 and the top mold 38 is
positioned on the powder layer 36.
[0062] Thereafter, the SPS sintering step is performed, which
serves to obtain an abradable layer 32 made directly on the shroud
sector 26. By way of example, the top mold 38 and the bottom mold
34 may be made of graphite. They may equally well be made of
tungsten carbide.
[0063] Before placing the shroud sector 26 in the bottom mold 34,
it is possible to deposit a layer of chemically inert material in
the bottom mold 34 and on the top mold 38. By way of example, the
chemically inert material may be boron nitride applied using a
spray. It is also possible to add boron nitride powder so as to
fill in the gaps present between the shroud sector 26 and the
bottom mold 34.
[0064] The chemically inert material may also be corundum.
[0065] Thereafter, the shroud sector 26 coated in the abradable
layer 32 is removed from the mold.
[0066] As shown in FIG. 4A, in order to make up a complete shroud
24, a plurality of shroud sectors 26 are assembled together, each
shroud sector 26 being covered in an abradable layer 32. Once these
turbine shroud sectors 26 have been assembled together, the
abradable layer 32 of each shroud sector presents a free surface 44
that need not necessarily extend continuously from the free surface
44 of the adjacent shroud sector 26. Thus, the free surfaces 44 of
the various shroud sectors 26 are machined so as to present a
machined surface 46 that is to face the turbine wheel. The machined
surface 46 presents as little discontinuity as possible.
[0067] Specifically, if any such discontinuity is present, then the
turbine wheel could strike against such a discontinuity, thereby
leading to impacts within the turbine, which is not desirable.
[0068] FIG. 5 is an image made with a scanning electron microscope
of an interface between a shroud sector 26 and an abradable layer
32. By way of example, this abradable layer 32 is sintered on the
shroud sector 26 at 950.degree. C., under a pressure of 40 MPa, for
30 minutes.
[0069] Pressure may be applied when cold, i.e. from the beginning
of the cycle, or when hot, during the period of sintering.
[0070] As can be seen in FIGS. 5 and 6, chemical composition varies
progressively along line 40 of FIG. 5, starting from the shroud
sector 26 and going towards the abradable layer 32, with a
diffusion zone 42 being defined at the interface between the shroud
sector 26 and the abradable layer 32.
[0071] FIGS. 7A-7D show various microstructures of abradable layers
32 presenting respective apparent porosities of about 10%, about
7%, about 3%, and practically zero.
[0072] It can thus be seen that by modifying the SPS sintering
parameters, such as temperature, pressure, and sintering time, it
is possible to obtain abradable layers 32 presenting structures
that are different. By way of example, FIG. 7A shows an abradable
layer 32 obtained during an SPS sintering step at 925.degree. C.
for 10 minutes while applying a pressure of 20 MPa. FIG. 7D shows
an abradable layer 32 obtained during an SPS sintering step at
950.degree. C. for 30 minutes while applying a pressure of 40
MPa.
[0073] It can be understood that the thickness of the abradable
layer 32 obtained after SPS sintering depends in particular on the
thickness of the powder layer 36 deposited on the inner surface 28
of the shroud sector 26 and on the SPS sintering parameters. The
thickness of the abradable layer 32 obtained after SPS sintering
may also depend on the grain size and on the morphology of the
powder used. In particular, the morphology of the powder may depend
on the method for manufacturing the powder. Thus, a powder
manufactured by gaseous atomization or by a rotating electrode has
grains of substantially spherical shape, while a powder
manufactured by liquid atomization has grains of shape that is less
regular.
[0074] Although the present disclosure is described with reference
to a specific implementation, it is clear that various
modifications and changes may be undertaken on those
implementations without going beyond the general ambit of the
invention as defined by the claims. Also, individual
characteristics of the various implementations mentioned above may
be combined in additional implementations. Consequently, the
description and the drawings should be considered in a sense that
is illustrative rather than restrictive.
* * * * *